The invention relates to a stamp, also referred to as a “die” or “die stamp,” for the micro contact printing and to a method for the production thereof.
The micro contact printing (Micro Contact Printing, μCP) refers to a method used for producing two-dimensional structures in the sub-micrometer range. According to A. Kumar and G. M. Whitesides, Features of gold having micrometer to centimeter dimensions can be formed through a combination of stamping with an elastomeric stamp and an alkanethiol “ink” followed by chemical etching, Applied Physics Letters, Volume 63, pp 2002-2004, 1993, liquid polymer silicon is poured for this over a structured relief, also called a master structure, and is then allowed to harden. The silicon elastomer forms a model of the topography of the mold in order to form a stamp. The stamp is then wetted with functionalized molecules, e.g. self-organizing alkanethiols, which take over the function of the “ink” during the stamping. As a result of direct contact with a substrate, the molecule pattern is transferred from the stamp to the substrate surface, analog to the high-pressure process.
Micro contact printing is simple and cost-effective and can be controlled quite easily for dimensions of the individual structures of approximately 200 nm. Below this dimension, however, the polydimethylsiloxane (PDMS) used for the stamp material reaches its mechanical limits. The resolution that can be achieved is limited by the effect of adhesion and capillary forces during the modeling and stamping. If the relief structures are too narrow, they can be modeled incompletely or can tear off when the stamp is pulled off. Structures with a high aspect ratio can tilt over, can adhere to each other, or can be flattened under pressure during the stamping. With a low aspect ratio, the adhering forces can result in the stamp being pushed through between two structures that are spaced apart too far. In addition, ink molecules can also diffuse through the gas phase onto the surface.
Different approaches have been pursued in recent years for creating structures with dimensions below 100 nm which, however, had to accept restrictions in the layout options for special structures or deal with the introduction of additional and complex process steps.
An attempt was made by H.-W. Li, B. V. O. Muir, G. Fichet, W. T. S. Huck, Nanocontact Printing, A Route to Sub-50-nm-Scale Chemical and Biological Patterning, Langmuir, Vol. 19, pp 1963-1965, 2003, to improve the mechanical stability through structures with a triangular cross section. To be sure, smaller lines were obtained in this way, but these had to be placed at greater distance to each other.
To reduce the intermediate spaces between two stamped surfaces, Y. Xia and G. M. Whitesides in Use of Controlled Reactive Spreading of Liquid Alkanethiol on the Surface of Gold To Modify the Size of Features Produced by Microcontact Printing, Journal of the American Chemical Society, Vol. 117, pp 3274-3275, 1995, experimented with a controlled spreading of the self-organized molecules during the stamping and in Extending Microcontact Printing as a Microlithographic Technique, Langmuir, Vol. 13, pp 2059-2067, 1997, experimented with a mechanical compression of the stamp.
To limit the diffusion of the self-organizing molecules through the gas phase onto the substrate and thus avoid having dull edges along the structures, L. Libioulle, A. Bietsch, H. Schmid, B. Michel, E. Delamarche in Contact-Inking Stamps for Microcontact Printing of Alkanethiols on Gold, Langmuir, Vol. 15, pp 300-304, 1999, did not impregnate the stamps, but used only wetted these with molecules on the active stamping surfaces, analog to the use of a stamping pad.
The document EP 1 193 056 A1 discloses a stamp of PDMS for the micro contact printing, which has a temporarily stable, hydrophilic surface that is produced by activating the stamp surface and providing it with a hydrophilic polymer.
The document EP 1 657 070 A1 discloses a stamp of an ionomeric polymer for the micro contact printing, as well as a method for the production of said stamp.
Each of the disclosed methods permits the reduction of a specific pattern characteristic, but does not allow either individually or in a combination the replication of optional patterns with structures having dimensions in the range below approximately 200 nm.
The documents DE 197 38 913 A1, U.S. Pat. No. 6,746,825 B2, and US 2006/0134556 A1, disclose structures on a thin substrate, which are produced through a phase separation of block copolymers. These structures respectively serve as a template, meaning they are sacrificed during one or more additional method steps in a following production process. However, these structures by themselves are not sufficient to reproduce a structure within the framework of a printing process.